Art of making propellant powder



Patented Feb. 28, 1950 ART OF MAKING PROPELLANT POWDER David. S. Bruce, Lawrence, Kans., and Eugene L. Klein, Kansas City, Mo., assignors, by mesne assignments, to the United States of America as represented by the Secretary of War No Drawing. Application July 19, 1945, SerialNo. 606,018

2 Claims.

This invention relates to a process of making smokeless powder, and more particularly to an improved method of incorporating dispersible materials in pulverulent form in a smokeless powder composition in the presence of water.

Smokeless powder usually consists of nitrocellulose or of a combination of nitrocellulose and nitroglycerin. In the explosives art, it has been known in the manufacture of smokeless powder to add to the one or two aforementioned constituents certain amounts of additional constituents for the purpose of modifying the sta bil'lty, "flash" characteristics, ballistics, and the like of the powder. V

In the copending U. S. application, Serial No. 517,549, filed January 8, 1944, by R. W. Cairns, now abandoned, it has been disclosed that the incorporation of an opaquing agent in the matrix of a thick web smokeless powder grain, for the purpose of rendering the powder substantially nontransparent to radiant energy, results in a powder grain which, when ignited in a jet-propelled device, will burn substantially uniformly and without sudden random increase in overall burning rate such as occurs when the powder is relatively transparent and permits passage of radiant energy in the form of rays of light and/or radiant heat as produced by the incandescent products of combustion of the smokeless powder.

In view of the deleterious effects of volatile solvents remaining in large grain powder and the difiiculties encountered in attempting to re- 'move adequately volatile solvents therefrom,

processes are used for the manufacture of thickweb, large-grain powders, in which volatile solvents are not used or in which they are removed prior to forming the grain. Such a process is that taught by Lundholm and Sayers, U. S. 438,816, and BritishPatent 10,376 of 1889. In this process, nitrocellulose was suspended in water, and then nitroglycerin, with or without other ingredients was added to the nitrocellulose accompanied by continuous agitation until the nitroglycerin was absorbed by the nitrocellulose. The resulting wet paste, as it is commonly termed, was then freed of water by suitable means and the product, with or without further drying, was malaxated (colloided) between rollers, preferably heated, or it was pressed, or subjected to the combined action of. pressure and heat. Other processes related thereto, wherein water is used as a mixing medium, have been developed.

7 .Thus, the teaching of theprior art onthe method of making smokeless powder, without the use of a volatile solvent, suggests two alternative methods of incorporating a dispersible material, for example, an opaquing agent, in the powder; namely, (1) mixing it with the other powder constituents in the water slurry prior to partial water separation therefrom as liquid water by screening, centrifuging and the like, or (2) mixing it with the partially or substantially completely dried powder when any water removed subsequently thereto is removed as water vapor. There are operational reasons for preferring to add the opaquing agent to the water slurry. However, because of the dispersibility of the agent in the water, a large portion of it is carried away by the water subsequently removed in the dewatering step. In some cases, this represents a loss of material. In the case of lamp black, even if there is an attempt to minimize the loss by recycling and reusing the separated water in a subsequent charge, it is difficult, if not almost impossible, to keep the equipment clean, a factor of the utmost importance in working with smokeless powder constituents.

Now, in accordance with the present invention, an improved process has been discovered for incorporating pulverulent material in a smokeless powder composition while the constituents of the powder are in dispersion in a fiuid dispersion medium and which is also a dispersion medium for the pulverulent material.

More specifically, it has been found that opaquing agents, such as lamp black, can be added to a water slurry of smokeless powder constituents and incorporated with the said constituents and a portion of the water separated subsequently as liquid water without the removal therewith of an appreciable proportion of the opaquing agent, by first making a dispersion of the opaquing agent in a nonvolatile, water-insoluble nitrocellulose plasticizer, adding the dispersion to the slurry, agitating until the plasticizer' has been adsorbed by the nitrocellulose. and partially dewatering by liquid separation. The resultant wet paste of powder is then dried and subsequently worked on rolls or the like to colloid the colloidable constituents and produce a colloided nitrocellulose-containing powder having an opaquing agent in pulverulent form uniformly distributed throughout the colloid.

Having now indicated in a general way. the

nature and purpose of the invention, there follows a more detailed description of a preferred embodiment thereof.

The composition utilized in the preferred embodiment of the invention had the following formulation:

The constituents were incorporated into the smokeless powder composition by the following process: The nitrocellulose was made into a dilute slurry in water. Then, with agitation, the nitroglycerin was added in a fine stream by means of a distributor. The addition required about 15 minutes, and stirring was continued for at least an additional minutes. This produced what will be referred to as a premix. The remaining ingredients, designated chemicals, were then added to the premix, agitation being maintained. The chemicals to be added were treated as follows: The carbon black was dispersed in the diethyl phthalate and added to the premix in the dispersed phase; the ethyl centralite and candelilla wax were homogenized in water and the resultant homogenized mass was added to the premix after the carbon black-diethyl phthalate add had been completed. The resulting mix was agitated for a full 30 minutes after all the chemicals had been added. This produced what will be referred to as a final mix.

The final mix was then dewatered in a centrifugal wringer and a wet paste obtained thereby having a water content of about 35%. The water separated from the powder in the wringer was substantially free of carbon black. Whereas, in a similar preparation, except that the carbon black was added to the slurry without first dispersing it in the plasticizer, a. large proportion of it was removed in the separated water.

The "wet paste was next dried by means of a forced hot air draft, to a water content of about 12-14%, and then colloided by working on a dif ferential speed roll assembly maintained at about 210 F. by means of circulating hot water through the rolls.

With reference to the preferred embodiment described above, considerable variation may be employed in the overall operation of the procedure as well as in the formulation employed, without departin from the spirit or scope of the invention. For example, other opaquing agents which are suitable for the purpose may be used in place of carbon black. Such agents include dyes of which nigrosine is an example, and opaque materials which have a light appearance in reflected light, such as titanium dioxide.

The quantity of the opaquing agent which may be used will depend somewhat on the nature of the material but, in general, will be within the range of 0.01-2.0% by weight of the total formulation.

Although diethyl phthalate is a preferred plasticizer in which to disperse the opaquing agent, other substantially nonvolatile liquid nitrocellulose plasticizers which are insoluble in water have been found to be suitable. The alkyl phthalates, such as diethyl phthalate, dibutyl phthalate, diamyl phthalate, and the like have been found to be particularly emcacious. The plasticizer used for dispersing the opaquing agent may be either six) a nonexplosive or an explosive substance. By explosive plasticizer is meant a substance such as nitroglycerin, nitroglycol, and the like. The amount of plasticizer to be used will depend upon its influence upon the ballistics and other characteristics of the resultant powder.

The method of incorporating the opaquing agent in the smokeless powder composition in accordance with this invention may be utilized at any stage in the preparation of the powder after the nitrocellulose has been suspended in water. In accordance with the method of this invention, a water-dispersible substance is added to and deposited upon nitrocellulose while in suspension in water, without having the water-dispersible substance contacted by the water. This is accomplished by dispersing the said substance in a water-insoluble, nonvolatile plasticizer for the nitrocellulose and mixing the resulting dispersion with the water slurry. The plasticizer maintains the substance (opaquing agent) out of contact with the water although mixed therewith. The plasticizer dispersion medium is gradually absorbed by the nitrocellulose, displacing the water, and the substance is deposited on the nitrocellulose where it is maintained with a layer of water repellent plasticizer protecting it from the water.

With further reference to the preferred embodiment of the invention described above, it is to be noted that the stabilizer, ethyl centralite, and the lubricating wax were added as an aqueous homogenized mass to the premix. The advantage in using this method of incorporating those ingredients in the powder is demonstrated by the results given in the table below showing the distribution of centralite in different powder charges wherein the centralite was incorporated in the powder by three different methods as indicated in the table. Samples of the powders contained the percentages of centr ahte as indicated.

TABLE Percentage dzstrzbutzon of centralite in powder samples Powder No. 1 Powder No. 2 Powder N o. 3

Percent Percent Percent l. 88 74 1. 06 67 1.04 1. 99 55 1. 10 93 38 1. 06 98 l. 47 l. 07 69 58 1. 06 41 51 1. 01 1. 16 3. l2 1. 07 54 73 l. 08 2. 23 86 l. 14 1. 15 43 1. 06 1. 02 99 1. 09 68 1. 57 1. 04 68 53 99 71 3. 20 1. 01 1. 20 66 9B 87 3. 24 1. 07 40 2. 00 1. 05 1. l1 1. 09 1. 00 66 66 1. 07

vera e 20 1. 5 Mean Deviation from 0 Av O. 45 0. 0. 02 Range of Variation. l. 84 2. 86 0. 16

Powder No. l-Centralite was mixed with D. E. P. in the normal manner and poured into the premix rapidly.

Powder No. 2-Centralite was mixed with D. E. P. and the chemicals poured into the premix very slowly.

Powder No. 3-Centralite was homogenized with water and poured into the premix after the D. E. I. had been added.

N om 1.D. E. P.=diethyl phthalate.

The method in accordance with this invention has its greatest utility when adding an opaquing agent to the nitrocellulose suspended in a large proportion of water, a portion of which water is to be removed subsequently as liquid water, such as by screening, decantation, and the like. However, it may be employed, with advantage of more uniform distribution, to add an opaquing agent to a wet nitrocellulose composition containing in the order of 30% or more water, such as an aqueous wet paste, when the water is to be removed subsequently only as water vapor, as in drying by hot air or indirect heating as when working on heated rolls.

The method of adding an opaquing agent, such as carbon black, to nitrocellulose suspended in water, is disclosed in accordance with this invention.

Thus, this invention has among its advantages the elimination of recycling the separated slurry water to recover the opaquing agent, cleaner operation, and better distribution of the opaquing agent, stabilizer and the lubricating wax with the nitrocellulose which results in more uniform incorporation in the colloided nitrocellulose after subsequent colloidization.

What We claim and desire to protect by Letters Patent is:

1. In the art of making propellant powder the process comprising treating a water suspension of a nitrocellulose-nitroglycerin mixture with a separately prepared dispersion of carbon black in a liquid dialkyl phthalate.

2. In the art of making propellant powder the process comprising treating a, water suspension of a nitrocellulose-nitroglycerin mixture with a separately prepared dispersion of carbon black in dlethyl phthalate.

DAVID S. BRUCE. EUGENE L. KLEIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,280,279 Nathan Oct. 1, 1918 1,338,691 Nathan May 4, 1920 1,909,991 Weihe May 23, 1933 1,966,327 Wood July 10, 1934 2,076,781 Jacobsen Apr. 13, 1937 2,291,082 Jarmus July 28, 1942 2,343,186 Hopkinson Feb. 29, 1944 2,344,516 McBride Mar. 21, 1944 2,408,252 de Ganahl Sept. 24, 1946 FOREIGN PATENTS Number Country Date 704,773 Germany Apr. 7, 1941 OTHER REFERENCES Explosives, by Marshall, vol. 1, page 326, published in 1917. 

1. IN THE ART OF MAKING PROPELLANT POWDER THE PROCESS COMPRISING TREATING A WATER SUSPENSION OF A NITROCELLULOSE-NITROGLYCERIN MIXTURE WITH A SEPRATELY PREPARED DISPERSION OF CARBON BLACK IN A LIQUID DIALKYL PHTHALATE. 